Monrrero is a fascinating piece of Chilean slang you'll find in modern reggaetón. It's derived from the verb monrrear, which means to dance perreo (a popular reggaetón dance style) in a very close and intense way.
In the song, FloyyMenor calls himself a monrrero when he says, "yo soy su monrrero" (I'm her intense dancer/charmer). He's styling himself as the expert partner the girl desires, perfectly capturing the specific vibe of the Chilean urban music scene with this one cool, hyperlocal word.
FloyyMenor's "CHICA ATRACTIVA" is a straight-up reggaeton track about being completely captivated by a girl. The whole song is built around the main idea: "Ella está activa, chica atractiva" (She's active, an attractive girl). He sees that she's interested in him, and he says, "eso me motiva" (that motivates me). He's into her style, calling her a "Chica bien fina" (a very fine girl), and the feeling she gives him is so intense he compares it to a drug, saying "Ella me flota como la ketafina" (She makes me float like ketamine).
He paints a picture of a relationship where they both like the same edgy lifestyle: "Me gustan las malas y te gustan los malo'" (I like bad girls and you like bad boys). He's ready to be her protector, promising to fight anyone who bothers her and spoil her with gifts like a trip to Europe. He even uses some specific Chilean slang, saying she likes "flaites que le hagan perreo" ('flaites' who dance perreo with her), which refers to a particular urban style from his home country. It's a song all about intense attraction, confidence, and a 'bad boy' fantasy.